Technical Field of the Invention

The present invention relates to a packaging bag with a perforation line, in particular a packaging bag having side panels with a patterned perforation line extending across a header region of the bag. The invention also relates to a method of forming a packaging bag having a line of perforations and to a perforation blade.

Background to the Invention

It is commonly known to form a packaging bag that is closed at a, usually, upper end by means of a sealed header region. In order to open the bag, the user must remove all or part of the header region by tearing the packaging material. To facilitate correct tearing of the material along a desired tear line, it is known to provide a line of perforations in the material. It may otherwise be difficult, or even impossible, for the average user to manually tear open the bag in a controlled manner. Incorrect tearing may result in the bag not being opened correctly making access to contents more difficult or it may result in the main body of the packaging bag being damaged so that it is no longer capable of usefully retaining product.

In many applications it is desirable for the user to be able to remove only one or some of the product contained in a packaging bag and to be able to re-close the bag so that the remaining product are safely retained. In some packaging bag arrangements, the header includes an outer header region closed by means of a permanent seal and an inner header region closed by means of a peelable and usually re-closable seal. In this arrangement, the user tears the packaging material to remove the outer header region and is then able to peel apart the inner header seal to gain access to the product in the bag. The user can re-close the seal in the inner header region to retain any remaining product pieces. It is particularly important with this type of header arrangement that the material is torn in a line between the inner and outer header regions. Incorrect tearing may result in the outer header region not being full removed and/or damage to the reclosable seal arrangements.

In a typical manufacturing process, a line of perforations is produced in a packaging bag using an elongate perforation blade having a number of perforation teeth. As each bag is formed in turn, the blade is advanced so that the teeth penetrate the material to form the perforation holes and is subsequently retracted. A common problem with known packaging bag arrangements is incorrect positioning of the line of perforations due to misalignment between the packaging bag and the perforation blade. For example, it is often advantageous if at least one perforation hole intersects a side edge of the bag so that it forms an open silt at the edge of the package. This makes it easier for a user to initiate tearing. Misalignment between the blade and the bag may result in there being no open slit at a side of the bag so that the user is forced to split the material at an edge of the bag to initiate tearing themselves. This is not always easy to do, especially with certain packaging materials used in the production of packaging bags that can be very tough to tear. The user may also have difficulty in initiating a tear at the correct position to align with the line of perforations. Proper alignment of the perforation blade is a particular issue when forming a line of perforations across the header region of a packaging bag having front and rear panels and side panels which are folded inwards between the front and rear panels in the header region, such as a quad seal bag. To form the header seal, the front and rear panels are bonded together in a central region between the inner fold lines of the side panels and are bonded to opposing inner surfaces of the side panels outside of the central region. In the outer edge regions, opposing outer surface regions of the folded side panels may also be bonded together, though this is not always the case. Accordingly, at the edges of the package where the tear is to be initiated there are four layers of material in the header region and the tear must extend across the inner fold lines of the side panels which might act to disrupt the line of tearing. It is especially important then with this type of packaging bag that a perforation hole intersect the edge of the bag on at least one side of the header to form an open slit that allows a user to initiate tearing. It is also advantageous that the line of perforations is suitably positioned and configured to ensure continuity of tearing across the inner fold lines of the side panels to reduce the risk of the tear propagating away from the desired tear line.

It is also desirable to have a blade arrangement which is suitable for use on a number of different machines which consistently produce the desired cuts in the bag even if the jaws are not perfectly aligned - thus enabling different machines to run with the same blades and all produce consistently opening packs.

It is an object of the present invention to at least alleviate one or more of the above problems.

Summary of the Invention In accordance with a first aspect of the invention, there is provided a packaging bag having a front panel, a rear panel, and a pair of side panels, the bag being closed along its upper edge by means of a sealed header region, the side panels being folded inwardly, at least within the header region, between opposing portions of the front and rear panels, the packaging having a line of perforations extending substantially laterally across the header region from one side of the packaging bag to the opposite side, the line of perforations comprising a plurality of spaced apart perforation holes arranged in a perforation pattern, wherein the perforation pattern comprises: a first pair of elongate perforation holes, each perforation hole in said first pair intersecting a respective side edge of the header region; a second pair of elongate perforation holes spaced inwardly from the first pair, each perforation hole in said second pair extending across an inner fold line of a respective one of the side panels; a first set of perforation holes located in spaced relation between the second pair of elongate perforation holes, each of the perforation holes in said first set having a length which is less than that of each of the elongate perforation holes in said second pair of elongate perforation holes; a second set of perforation holes located in spaced relation between one of the elongate perforation holes in the second pair of elongate perforation holes and a respective one of the elongate perforation holes of the first pair of elongate perforation holes on one side of the bag; and a third set of perforation holes spaced between the other of the elongate perforation holes in the second pair of elongate perforation holes and a respective one of the elongate perforation holes of the first pair of elongate perforation holes on an opposite side of the bag; each of the perforation holes in the second and third sets having a length which is less than that of the perforation holes in the second pair of elongate perforation holes.

Each of the perforation holes in the second and third sets of perforation holes may have a length which is less than the length of the perforation holes in the first set. All the perforation holes in the second and third sets may be substantially the same length. There may be three perforation holes in each of the second and third sets of perforation holes.

At least one of the perforation holes in the first set of perforation holes may have a length that is different from at least one other of the perforation holes in the first set. The perforation holes in the first set may include an outer pair of perforation holes having a first length and a plurality of perforation holes located in spaced relation between the outer pair that have a different length from the outer pair. The perforation holes in the outer pair may be shorter in length than the remaining perforation holes in the first set. There may be three perforation holes located in spaced relation between the outer pair in the first set.

At least one of the perforation holes can be configured to propagate tearing in a desired direction across the header region. At least one of the perforation holes may have an apex at one end at least to control the direction of tear. Said at least one perforation hole may be generally triangular in shape having an apex at one end and a base side opposite the apex. Alternatively, said at least one perforation hole may be a parallelogram/rhomboid, having an apex at either end. At least the perforation holes in the second and third sets may be configured to propagate tearing in a desired direction across the header region. The perforation holes in the second and third sets may be triangular in shape, all having an apex directed generally towards the same side edge of the header region.

The perforations holes may be arranged substantially in-line and/or generally parallel with one another.

The packaging bag may be a quad seal bag.

In accordance with a second aspect of the invention, there is provided a perforation blade for producing a line of perforations in a packaging bag in accordance with the first aspect. In accordance with a third aspect of the invention, there is provided a perforation blade comprising an elongate base and a plurality of spaced perforation teeth projecting from base, the perforation teeth comprising: a first pair of elongate perforation teeth arranged one at either end of the blade; a second pair of elongate perforation teeth spaced inwardly from the first pair, the teeth in the second pair having a length which is less than that of the teeth in the first pair; a first set of perforation teeth located in spaced relation between the second pair of elongate perforation teeth, each of the teeth in the first set having a length which is less than that of the teeth in the second pair of elongate teeth; a second set of perforation teeth located in spaced relation between one of the teeth in the second pair of elongate perforation teeth and a respective tooth of first pair of elongate perforation teeth on one side of the blade; and a third set of perforation teeth located in spaced relation between the other tooth in said second pair of elongate perforation teeth and the respective elongate perforation tooth of the first pair of elongate perforation teeth at an opposite side of the perforation blade, each of the perforation teeth in the second and third sets having a length which is less than that of the perforation teeth in the second pair of elongate perforation teeth.

Each of the perforation teeth in the second and third sets of perforation teeth may be of a length which is less than the length of the perforation teeth in the first set. All the perforation teeth in the second and third sets may be substantially the same length. There may be three perforation teeth in each of the second and third sets of perforation teeth.

At least one of the perforation teeth in the first set of perforation teeth may have a different length from at least one other of the perforation teeth in the first set. The perforation teeth in the first set may include an outer pair of perforation teeth having a first length and a plurality of perforation teeth located in spaced relation between the outer pair that have a different length from the outer pair. Each of the perforation teeth in the outer pair of the first set may be shorter in length than the remaining perforation teeth in the first set. There may be three perforation teeth located in spaced relation between the outer pair in the first set.

At least one of the perforation teeth may be shaped to form a perforation hole having an apex at one end. Said at least one perforation tooth may be shaped to produce a generally triangular perforation hole having an apex at one end and a base side opposite the apex. Alternatively, said at least one perforation tooth may be shaped to produce a parallelogram/rhomboid shaped perforation hole having an apex at either end. At least the perforation teeth in the second and third sets may be shaped to produce perforation holes having an apex at one end at least. The perforation teeth in the second and third sets may be triangular in shape, all having an apex directed generally towards the same side edge of the blade.

At least one of said perforation teeth may have chamfering provided at either or both ends thereof, and/or on either or both sides thereof. Said chamfering may have any suitable shape and dimension. By chamfering said at least one perforation tooth, the shape of the perforation hole cut by said perforation tooth may adapted to any suitable shape, including but not limited to triangular, rhomboid, trapezoid, or any non-rectangular polygonal. In one embodiment, said chamfering may be provided on both sides of one end of the at least one perforation tooth, said chamfering extending substantially the entire length of the perforation unit, thereby resulting in a triangular perforation hole. In an alternative embodiment, said at least one perforation tooth may have chamfering provided on both ends but on opposing sides, so as to cut a rhomboid or diamond-shaped perforation hole.

The elongate perforation teeth in the first pair of elongate teeth may each have a length which is in the range of 1/5 to 1/8, in particular 1/6 to 1/7, of the overall width of the blade.

The elongate perforation teeth in the second pair of elongate teeth may each have a length which is in the range of 1/8 to 1/10, in particular 1/9, of the overall width of the blade. The elongate perforation teeth in the second pair of elongate teeth may each have a length which is 4 to 6, more particularly 5, times the length of the teeth in the second and third sets of perforation teeth.

The elongate perforation teeth in the second pair of elongate teeth may each have a length which is 1.6 to 2, more particularly 1.8, times the length of the longest teeth in the first set of perforation teeth.

The elongate perforation teeth in the second pair of elongate teeth may each have a length which is 2 to 4, more particularly 2.5 to 3.5, times the length of the shortest teeth in the first set of perforation teeth. The perforation teeth may be arranged substantially in-line and/or generally parallel with one another.

In accordance with a fourth aspect of the invention, there is provided a method of manufacturing a packaging bag in accordance with the first aspect of the invention using a perforation blade according to either of the second and third aspects of the invention, the method comprising forming the packaging bag from a length of foldable material and producing a header region closing one end, aligning the perforation blade so as to extend in a lateral direction of the packaging bag across the header region and bringing the perforation blade into contact with the material in the header region and applying pressure so that the perforation teeth penetrate the material to form a line of perforations extending across the header region, the blade being aligned so that each of the perforation teeth in the second pair of elongate perforation teeth extend across the inner fold line of a respective one of the side panels so as to form a perforation hole which extends across the inner fold line. The blade may be aligned so that each of the perforation teeth in the first pair of elongate perforation teeth extends across a respective side edge of the header region so as to form an open slit on either side.

Detailed Description of the Invention In order that the invention may be more clearly understood embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 is view from the front of an embodiment of a packaging bag according to a first aspect of the present invention; Figure 2 is a view from one side of the packaging bag of Figure 1;

Figures 3 A and 3B are perspective views of the packaging bag of Figure 1 showing the bag before and during opening;

Figure 4 is a plan view of an embodiment of a perforation blade according a second aspect of the present invention; Figures 5a to 5e are a series of schematic drawings illustrating how the propagation of a tear can be controlled by shaping the perforation holes; and

Figures 6a to 6d are detailed schematic views of perforation teeth forming part of the perforation blade of Figure 4, illustrating alternative tooth profiles for producing differently shaped perforation holes. A packaging bag 10 in accordance with a first aspect of the invention is shown in Figures 1 to 3. The packaging bag 10 according to the present embodiment is a quad seal type bag having a front panel 11, a back panel 12 (not visible), and two opposing side panels 13 (only one shown). The upper end of the packaging bag is closed by means of a sealed header 14. Seams 9 are formed at all four corners where the side panels meet the front and rear panels. This configuration allows the bag 10 to be stood upright on its base for display and storage purposes. This is a popular packaging arrangement for a range of products including consumable products. However, the invention is not limited to application with quad seal bags but can be applied more generally to packaging bags (including pouches) of a range of types, especially packaging bags having side panels that are folded inwardly between front and rear panels in a header region. The packaging bag 10 is formed from a length of flexible material which is folded and joined together along various seems in a known manner. The packaging bag 10 can be formed from any suitable material known in the art including laminated materials. Suitable materials include, but are not limited to: polymeric materials, metallic foil, and paper. Packaging bags 10 in accordance with the invention can be manufactured using a form fill seal (FFS) machine which produces a number of bags in turn from a roll of material in a relatively high speed and substantially continuous process. Each bag is formed by taking a length of the material which is folded and sealed to form a pouch open at an upper end. The product is introduced into the partly formed bag through the open upper end which is subsequently sealed to form the header region 14 closing the bag. During the forming and filling process, each bag is separated from the remainder of the material on the roll using a knife. In some cases, the packaging bag also has seal along the bottom of the bag. With this type of packaging bag, the contents may be introduced into the bag through the bottom before the bottom seal is formed. In which case, the header region 14 is formed before the contents are introduced.

The side panels 13 are folded inwardly, at least in the header region 14, so that each side panel has a substantially vertical inner fold line (indicated by the dashed lines 15, 16) formed substantially in the middle of the panel. To produce the sealed header region 14, opposing inner surfaces of the front and front and rear panels 11, 12 are sealed together in a central region between the inner fold lines 15, 16. In the regions outside of the inner fold lines 15, 16, the front and rear panels 11, 12 are each sealed to the opposing inner surfaces of the respective side panel 13. The opposed outer surfaces regions of each of the side panels 13 may be bonded together in the header region so as to form a single elongate sealed header region 14 extending laterally across the full width of the bag. However, this is not always the case and the opposed outer surface regions of the folded side panels 13 may be left un-bonded so that at each side of the bag the header is bifurcated. The seals in the header region 14 may be formed using an adhesive to bond the opposing surfaces of the material or by heating the material under pressure so that the opposing surfaces melt and fuse together to form a welded seal or by any other suitable method.

To open the packaging bag 10, the user tears off at least an outer part 14A of the sealed header region 14 as illustrated in Figure 3 A. To assist the user in this, a line of perforations 17 extends laterally across the header region 14 below the sealed outer part 14 A. The inner part 14B of the header below the line of perforations 17 may not be sealed so that the packaging bag 10 is open once to outer header part 14A has been removed. Alternatively, the inner part 14B of the header may be closed by means of a peelable seal so that the packaging bag 10 remains closed even on removal of the outer header part 14 A. To open the package, the user removes the outer part 14A of the header by tearing along the line 17 of perforations and is then able to peel apart the seal in the inner header part 14B to gain access to product in the bag. Typically the seal in the inner header part 14B is reclosable so that the user can reclose the bag after removing one or some of the product. The seal in the inner part 14B of the header could be formed using a peelable and re-sealable adhesive such as a cold seal or it may comprise a mechanical seal arrangement such as a zipper or press-fit seal. The seal in the outer part 14A of the header is typically a permanent seal, that is to say the seal cannot be easily pulled apart without damaging the material, and may be formed using a permanent adhesive or by welding.

A suspension opening 18 is provided in the outer part 14A of the header region to allow the package to be suspended from a hook for display purposes. The suspension hole may be shaped to allow the packaging bag 10 to be suspended from a Euro-hook as shown but any suitably shaped suspension opening 16 can be provided. The line of perforations 17 is configured so that the user is able to tear the material easily along a desired tear path but also so that seal of the packaging bag 10 is not compromised before opening and so that the material does not unintentionally burst along the line of perforations prior to opening, particularly when the filled packaging bag 10 is suspended by means of the suspension opening 16. As can be seen best from Figure 1, the line of perforations 17 includes a plurality of perforation holes of different length arranged in a perforation pattern. The perforation pattern includes a first pair of elongate perforation holes 19, each of which intersects a respective side edge of the header region to form an open slit. A second pair of elongate perforation holes 20 are spaced inwardly from the first pair and are positioned so that each of the perforation holes 20 in the second pair extend across an inner fold line 15, 16 of a respective one of the side panels 13. A first set of perforation holes 21a, 21b are located in spaced relation between the second pair of elongate perforation holes 20. Each of the perforation holes 21a, 21b in the first set have a length (measured in a transverse direction of the bag, i.e. the direction of arrow A in Figure 1) which is less than that of the elongate perforation holes 20 in the second pair of elongate perforation holes. A second set of perforation holes 22 are located in spaced relation between one of the elongate perforation holes 20 in the second pair of elongate perforation holes and a respective one of the elongate perforation holes 19 of the first pair of elongate perforation holes on one side of the bag and a third set of perforation holes 23 are located in spaced relation between the other of the elongate perforation holes 20 in the second pair of elongate perforation holes and a respective one of the elongate perforation holes 19 of the first pair of elongate perforation holes on an opposite side of the bag. Each of the perforation holes 22, 23 in the second and third sets have a length which is less than that of the perforation holes 20 in the second pair of elongate perforation holes.

The perforation pattern as described above has a number of advantages. The first outer pair of elongate perforation holes 19 form open slits at either side of the bag. This assists a user to initiate tearing along the line of perforations 17 at the outer edges where there are four layers of material due to the folded in side panels. The second pair of elongate perforation holes 20 assist the line of tearing to propagate in the desired direction across the inner fold lines 15, 16 of the side panels. If the perforation holes 20 did not extend across the inner fold lines 15, 16, there is a risk that the tear would be deflected away from the desired tear direction as it crosses an inner fold line 15, 16 particularly in the transition from the central region to an edge region where the thickness of material increases from two layers to four. The perforation holes 21a, 21b, 22, 23, in the first, second and third sets are all shorter than the elongate perforation holes 20 of the second pair of elongate perforation holes, with the perforation holes 21a, 21b in the first set being longer than the perforation holes 22, 23 in the second and third sets. There are five perforation holes 21a, 21b in the first set. The outer two perforation holes 21a being shorter in length than the inner three perforation holes 21b. In each of the second and third sets, there are three perforation holes 22, 23 all of which are substantially the same length and identical in shape.

It will be noted that the perforation holes are arranged substantially in-line with one another and extend generally parallel to one another.

A perforation blade 30 for forming the line of perforations 17 is shown in Figure 4. The blade has an elongate base 31 having projections 3 la on a rear edge for mounting the blade in a FFS or other suitable machine. A number of spaced apart perforation teeth project from a forward or cutting edge of the blade for inserting into the material of the header region 14 of the bag 10 to form the perforation holes. Each of the teeth may have a series of small projections or serrations along a forward edge to help the teeth pass through the material in the header region.

The perforation teeth on the blade 30 are arranged and configured in a pattern conforming to the perforation pattern formed in the bag 10 as described above. Accordingly, the blade 30 has a first pair of elongate perforation teeth 32 at either side of the blade for forming the first pair of elongate perforation holes 19. A second pair of elongate perforation teeth 33 is spaced inwardly from the first pair 32 for forming the second pair of elongate perforation holes 20 in the bag. A first set of perforation teeth 34a, 34b are located in spaced relation between the second pair of elongate perforation teeth 33 for forming the first set of perforation holes 21a, 21b. A second set of perforation teeth 35 are located in spaced relation between one of the elongate perforation teeth 33 in the second pair of elongate perforation teeth and a respective one of the outer elongate perforation teeth 32 for forming the second set of perforation holes 22, 23. A third set of perforation teeth 36 are located in spaced relation between the other of the elongate perforation teeth 33 in the second pair of elongate perforation teeth and the other outer elongate perforation tooth 32 on the other end of the blade for forming the third set of perforation holes 22, 23.

The perforation teeth on the blade conform generally in size and shape to the perforation holes in the line of perforations 17 in the bag, though it should be noted that the first pair of elongate teeth 32 are considerably longer than the elongate teeth 33 of the second pair. Since outer pair of elongate teeth 32 intersect the side edges of the header region, the perforation holes or slits 19 they produce are shorter than the perforation holes 20 produced by the teeth 33 in the second pair. Each of the perforation teeth 34a, 34b in the first set have a length (measured in a transverse direction of the blade) which is less than that of the elongate perforation teeth 33 in the second pair of elongate perforation teeth. There are five perforation teeth in the first set, the outer two 34a having a length which is less than the length of the middle three teeth 34b. Each of the teeth 35, 36 in the second and third sets are shorter than the elongate perforation teeth 33 in the second pair of elongate perforation teeth 20 and the teeth 34a, 34b in the first set. All the teeth 35, 36 in the second and third sets are substantially the same length.

It is a particular advantage of the blade 30, that the first and second pairs of elongate teeth 32, 33 are considerably longer than are used in conventional perforation blades as this allows for a degree in process variability in aligning the blade 30 with the header region whilst ensuring that open slits are formed at either side of the header and the positioning of perforation holes that extend across the inner fold lines 15, 16 of the side panels to improve tearing ability. In the present embodiment, the blade 30 has a width W of about 237mm. The outer elongate teeth 32 are each approximately 40mm in length, representing about 1/6 of the overall width of the blade. The second pair of elongate perforation teeth 33 are each approximately 25mm in length which represents approximately 1/9.5 of the overall width of the blade. As discussed above, the provision of unusually long perforation teeth 33 for the second pair of elongate perforation teeth allows for a reasonable degree of process variation in the alignment of the blade 30 with the header 14 whilst ensuring that they extend across the inner fold lines 15, 16 of the side panels. Surprisingly, it has been found that the resultant large perforation holes 20 do not compromise the integrity of the packaging bag and do not result in the bag unintentionally bursting along the line of perforations prior to opening as might have been expected.

The teeth 35, 36 in the second and third sets have a length of approximately 5mm so that the elongate teeth 33 in the second pair have a length which is approximately 5 times the length of the teeth in the second and third sets. The outer teeth 34a in the first set are approximately 8mm in length and the middle teeth 34b in the first set are approximately 14mm in length, so that the teeth 33 in the second pair of elongate teeth have a length which is approximately 1.8 times the length of the central teeth 34b and 3 times the length of the smaller outer teeth 34a in the first set.

It will be appreciated that the actual dimensions of the blade 30 and the various perforation teeth can be varied as required but the second pair of elongate perforation teeth 33 should be significantly longer than any of the other perforation teeth between the two outer elongate teeth 32 and are longer than are conventionally used to form perforations in a packing bag of the general type disclosed. It will also be noted that the perforation teeth are arranged substantially in-line with one another and extend generally parallel to one another.

In order for a tear to propagate along a line of perforations, the perforation holes must be dimensioned and spaced sufficiently closely together that the tear extends through the material from one perforation hole to the next. The direction of tear can also be affected by the direction of force applied by the user. If the user does not apply a force generally in line with the line of perforations, there is a risk that the tear may propagate away from the desired direction of tear along the line of perforations.

Figure 5a illustrates schematically a number of conventional perforation holes 37 forming part of a line of perforations. Each perforation hole 37 is substantially rectangular and is spaced apart from adjacent holes 37. When opening a packaging bag, a tear is normally initiated at one side of the package by the application of a tearing force as indicated by the arrow 38. In an ideal situation, so long as a sufficient tearing force is applied, the tear propagates from each perforation hole 37 to the next in turn along the line as indicated by the arrows 39.

In reality, a number of factors may cause a tear to deviate from the ideal direction. The packaging bag material may contain imperfections or regions of varying strength/toughness may be present due say to the process of forming a seal or a suspension opening in the material or where there are changes in the thickness of the material. Additionally, the user may apply a tearing force at an angle to the line of perforations. Figure 5b illustrates schematically how a tear 39 may propagate from the end of one perforation hole in a direction so as to miss the next perforation hole. Should this happen in the line of perforation 17 in the bag 10, it may result in the outer header region 14 A not being fully removed or in the main body of the bag or the inner header seal 14B being torn.

Figures 5 c to 5e illustrate how perforation holes can be shaped in order to control direction of tear and so encourage a tear 39 to propagate in a desired direction from one perforation hole to the next along a line of perforations. In Figure 5c, the perforation holes 40 are triangular each having an apex 41 which is aligned in the desired direction of tear 42, i.e. in a lateral direction from right to left as shown in the Figure. Each of the perforation holes 40 has a base edge 43 opposite the apex which extends generally perpendicularly to the desired direction of tear, which in this case is parallel to a side edge of the bag. When a user performs a tearing operation, the tear will tend to originate at the apex of one perforation hole 40 and travel in a direction towards the base 43 of the next perforation hole in the line. This arrangement allows the tear to propagate from the apex 42 of one perforation hole 40 at a relatively large range of angles whilst still travelling towards and intersecting the base 43 of the adjacent perforation hole. Accordingly, the risk of the tear 39 propagating away from the line of perforations is reduced.

One potential drawback with the use of triangular perforation holes 40 as illustrated in Figure 5c is that the tear can only reliably be produced in one direction along the line of perforations, from right to left as shown. This would require the user to always tear the bag in the correct direction which cannot be guaranteed despite placing guidance on the packaging to indicate the required direction of tear. Figures 5d and 5e illustrate an alternative arrangement which would allow a tear to be produced in either direction along the line of perforations. In the arrangement illustrated in Figures 5d and 5e, the perforation holes 44 have a parallelogram/rhomboid shape arranged to that each hole has an apex 45 at either end. As illustrated in Figure 5d, if torn in a direction from right to left, the tear 39 will tend to propagate from the apex on the left hand end of each perforation hole toward the right and end of the adjacent perforation hole. Figure 5e illustrates propagation of a tear line in the opposite direction from left to right.

Perforation holes having other non-rectangular shapes can also be adopted to control the direction of tear. Suitable shapes will typically have an apex at one or both ends of the perforation hole and a relatively large width dimension either at the opposite end of the perforation hole from the apex or in a region between the ends. Possible shapes include, without limitation, diamond shape, pentagonal shape, hexagonal shape, or other polygonal shapes.

The above techniques for controlling the direction of tear can be adopted in a packaging bag 10 in accordance with the invention in which any of the perforation holes could be shaped as discussed above to control the direction of tear. It is particularly advantageous is the perforation holes in the second and third sets of perforations are shaped to control the direction of tear as in these regions the material in the header is four layers thick and there is a greater risk that the tear may propagate away from the line of perforations. Accordingly, the perforation holes 22, 23 in the second and third sets may be triangular, each perforation hole having an apex aligned with (pointing in) a desired direction of tear, which in the present embodiment is laterally across the header from right to left as shown, and having a base opposite the apex aligned generally perpendicular to the desired direction of tear, which in this case is substantially parallel to a side edge of the bag. Alternatively, the perforation holes 22, 23 in the second and third sets could have a parallelogram/rhomboid shape with an apex at either end to allow the tear to be formed in either direction along the line of perforations or any of the other shapes proposed above.

In order to produce perforation holes 22, 23 having a non-rectangular shape, the corresponding teeth of the perforation blade are chamfered at one or both ends and on either or both sides, dependent on the desired shape of the resulting perforation hole. For example, Figure 6a illustrates a perforation tooth 46 that is chamfered 47 at one end and on both sides thereof so as to have a triangular in shape when viewed from the front as illustrated in Figure 6b for forming a perforation hole that is correspondingly triangular in shape. Figure 6c illustrates a perforation tooth 48 that is chamfered 49 at both ends and on opposite sides so as to have a parallelogram/rhomboid shape as illustrated in Figure 6d for producing a perforation hole having a corresponding parallelogram/rhomboid shape. By varying the placement and the dimensions of chamfering it is of course possible to vary the shape of the perforation tooth and according the shape of the resultant perforation hole.

The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.